Eer High Frequency Amplifier

ABSTRACT

An EER high frequency amplifier wherein the dynamic range of the gain can be widened by performing a predetermined control of a device in a high frequency amplifying part and thereby enhancing the isolation within the device. In an EER high frequency amplifier ( 1 ), an envelope detecting part ( 2 ) extracts an amplitude signal from an input high frequency signal, while a limiter ( 3 ) extracts a phase signal therefrom. A baseband amplifying part ( 4 ) generates a voltage in accordance with the amplitude signal and supplies it as the drain voltage of a GaAs FET ( 5   a ) of a high frequency amplifying part ( 5 ). When the drain voltage is below a predetermined first reference voltage, a gate voltage control part ( 6 ) holds an initially established gate voltage. When the drain voltage exceeds the first reference voltage, the gate voltage control part ( 6 ) so controls the gate voltage as to be proportional to the drain voltage. Moreover, when the drain voltage is above a second reference voltage that is higher than the first reference voltage, the gate voltage control part ( 6 ) holds the initially established gate voltage. When the drain voltage is below the second reference voltage, the gate voltage control part ( 6 ) so controls the gate voltage as to be proportional to the drain voltage.

TECHNICAL FIELD

The present invention relates to an EER high frequency amplifier thatcarries out amplification and amplitude modulation by receiving anamplitude signal and controlling a power supply voltage.

BACKGROUND ART

Conventionally, in wireless communication equipment or the like, anamplification scheme has been proposed that uses an EER (EnvelopeElimination and Restoration) modulation amplifier having high-efficientmodulation and amplification performance. This EER modulation amplifieramplifies a high frequency signal using a class B or class E saturatedamplifier, and further carries out amplitude modulation by inputting theamplitude signal to a power supply terminal of an amplification sectionin the last of the saturated amplifier. Therefore, this EER modulationamplifier has a complex function where a modulation function is added toa linear amplification function of the original high frequency amplifier(for example, see Patent Document 1). In this type of the EER highfrequency amplifier, a high frequency amplification section amplifiesonly the phase signal which does not include amplitude information, and,for example, the high frequency amplification section configured withgallium arsenide FET (GaAs FET) carries out amplitude modulation bycontrolling the drain supply voltage according to the amplitude signalbased on the change in gain of GaAs FET according to the drain voltage.According to this configuration, the high frequency amplificationsection does not amplify the amplitude signal, so that it is possible touse a high-efficient saturated amplifier for the high frequencyamplification section. As a result, it is possible to improve efficiencyof the EER high frequency amplifier.

FIG. 1 is a schematic configuration diagram of a conventionally used EERhigh frequency amplifier. In FIG. 1, when a high frequency signal isinputted to EER high frequency amplifier 10, the high frequency signalis broken down into polar components of the amplitude component and thephase component through envelope detection section 11 and limiter 12.Then, the broken down amplitude component and phase component flowthrough different paths (that is, amplitude signal path 13 and phasesignal path 14), and are separately amplified. That is, when the phasesignal flowing through phase signal path 14 is amplified at highfrequency amplification section 16, and the amplitude signal flowingthrough amplitude signal path 13 is amplified at baseband amplificationsection 15, the amplitude signal amplified at baseband amplificationsection 15 becomes a power supply voltage of high frequencyamplification section 16, and thereby high frequency amplificationsection 16 carries out amplitude modulation, recombines the amplitudecomponent and the phase component, and outputs a linearly-amplified highfrequency signal.

However, with an actual EER high frequency amplifier, unless a width ofthe dynamic range of gain fluctuation of high frequency amplificationsection 16 due to a change of the power supply voltage is ensured wideenough for the amplitude component, it is not possible to accuratelyindicate the amplitude signal which should be originally generated, and,as a result, a desired high frequency signal cannot be outputted.Therefore, high frequency amplification section 16 must realize a widedynamic range. In particular, when the power supply voltage is madelower, and gain of high frequency amplification section 16 is madelower, leak of an input signal to the output side due to insufficiencyof the isolation between the input and the output of high frequencyamplification section 16 becomes prominent, and therefore the dynamicrange of gain with respect to the power supply voltage may berestricted.

As a measure to improve insufficiency of the isolation, a method isknown where a metal plate is inserted between the input and the outputof the high frequency amplifier to prevent electrical coupling betweenthe input and the output because of space. FIG. 2 is a conceptualdiagram for improving the isolation between the input and the output inthe conventional high frequency amplifier. As shown in FIG. 2, metalshield plate 20 is provided between the input and the output of highfrequency amplifier 17, and input signal line 18 and output signal line19 are isolated from the high frequency signal. That is, it is possibleto improve the isolation by suppressing spatial electrical couplingbetween the input and the output of high frequency amplifier 17 usingmetal shield plate 20 (for example, see Non-Patent Document 1).

Further, a method is known for improving the isolation by providing animpedance matching circuit at the input or interstage of the highfrequency amplifier, and providing a voltage variable element in thisimpedance matching circuit. According to this technique, it is possibleto change a ratio between a reflected wave and a traveling wave (thatis, SWR) by changing a constant of the voltage variable element of theimpedance matching circuit using a control voltage, and reduce a leaksignal to the output side by suppressing the quasi input signal bysubstantially increasing the SWR, so that it is possible to improve theisolation (for example, Patent Document 2).

Patent Document 1: Japanese Patent No. 3207153

Patent Document 2: Japanese Patent Application Laid-Open No. HEI8-222973

Non-Patent Document 1: “New Low Frequency/High Frequency Circuit DesignManual” Masaomi Suzuki, CQ Publishing, 1998

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, with the above-described technique of Non-Patent Document 1, aphysical shield measure is taken which uses a metal shield plateprovided between the input and the output of the high frequencyamplifier, and therefore a shield effect can be obtained only in thecase of spatial coupling between the input and the output of the highfrequency amplifier. Therefore, it is not possible to substantiallyimprove the isolation including the isolation of space and the isolationbetween lines, and therefore the increase of the dynamic range of gainof the high frequency amplifier is limited. Further, with theabove-described technique of Patent Document 2, it is not possible toimprove the isolation inside the device used for the high frequencyamplifier, and therefore the dynamic range of gain cannot besubstantially increased.

It is therefore an object of the present invention to provide an EERhigh frequency amplifier with the improved isolation inside the deviceby carrying out predetermined control on the device used for the highfrequency amplification section, and the increased dynamic range of gainof the high frequency amplification section.

Means for Solving the Problems

An EER modulation amplifier of the present invention outputs a desiredmodulated and amplified signal from a high frequency amplificationsection by separating a phase signal and an amplitude signal from aninputted high frequency signal, amplifying the signals individually, andcontrolling a drain voltage of the high frequency amplification sectionbased on the amplified amplitude signal, the EER modulation amplifieremploys a configuration having: a drain voltage generating section thatgenerates a drain voltage according to the amplitude signal and suppliesthe drain voltage to a drain terminal of the high frequencyamplification section; a drain voltage determining section thatdetermines a magnitude of the drain voltage generated by the drainvoltage generating section in comparison to a predetermined referencevoltage; and a gate voltage control section that controls a gate voltageof the high frequency amplification section according to the magnituderelationship between the reference voltage and drain voltage determinedby the drain voltage determining section.

Furthermore, the EER modulation amplifier of the present inventionemploys a configuration wherein: the reference voltage is formed with afirst reference voltage and a second reference voltage which has ahigher voltage level than the first reference voltage; and the gatevoltage control section holds an initially set gate voltage when thedrain voltage is determined to be lower than the first referencevoltage, and controls the gate voltage in proportion to the drainvoltage when the drain voltage is determined to be higher than the firstreference voltage and lower than the second reference voltage.

Furthermore, the EER modulation amplifier of the present inventionemploys a configuration wherein: the gate voltage control section holdsan initially set gate voltage when the drain voltage is determined to behigher than the second reference voltage, and controls the gate voltagein proportion to the drain voltage when the drain voltage is determinedto be lower than the second reference voltage and higher than the firstreference voltage.

Still further, the EER modulation amplifier of the present inventionemploys a configuration wherein: the drain voltage determining sectiondirectly detects the amplitude signal separated from the high frequencysignal and determines the magnitude of the amplitude signal incomparison to the reference voltage, instead of determining themagnitude of the drain voltage in comparison to the reference voltage.

ADVANTAGEOUS EFFECT OF THE INVENTION

According to the present invention, by comparing the drain voltage ofthe high frequency amplification section and a predetermined referencevoltage, and, when the drain voltage is lower than (or higher than) thereference voltage, controlling the gate voltage of the device used forthe high frequency amplification section, gain of the device issuppressed, and the isolation inside the device is improved. By thismeans, it is possible to increase the dynamic range of gain of the highfrequency amplification section. That is, by controlling the gatevoltage according to the drain voltage, the isolation between the inputand the output of the high frequency amplification section is improved,so that it is possible to increase the dynamic range of gain of the highfrequency amplification section without adding components.

Furthermore, according to the present invention, the isolation betweenthe input and the output of the device (for example, GaAs FET)configuring the high frequency amplification section changes accordingto the gate voltage, and therefore, when the drain voltage of the highfrequency amplification section is lower than the predetermined firstreference voltage, the initially set gate voltage is held, and, when thedrain voltage is higher than the first reference voltage, the gatevoltage is controlled in proportion to the drain voltage. By controllingthe gate voltage in this way, it is possible to improve the isolationand increase the dynamic range of gain of the high frequencyamplification section.

Further, according to the present invention, when the drain voltage ofthe high frequency amplification section is higher than the secondreference voltage which is set at a higher level than the firstreference voltage, the initially set gate voltage is held, and, when thedrain voltage is lower than the second reference voltage, the gatevoltage is controlled in proportion to the drain voltage. By controllingthe gate voltage in this way, even if the drain voltage is at highlevel, it is possible to improve the isolation and increase the dynamicrange of gain of the high frequency amplification section.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a conventionally used EERhigh frequency amplifier;

FIG. 2 is a conceptual diagram for improving the isolation between theinput and the output of the conventional high frequency amplifier;

FIG. 3 is a configuration diagram of an EER high frequency amplifieraccording to an embodiment of the present invention;

FIG. 4 is a characteristic diagram showing a relationship of gain to agate voltage of GaAs FET realized by the EER high frequency amplifier ofFIG. 3;

FIG. 5 shows an example of a circuit configuration inside the gatevoltage control section of FIG. 3; and

FIG. 6 is a characteristic diagram as a result of experiment ofimproving the dynamic range when the circuit of the gate voltage controlsection shown in FIG. 5 is used.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention has a feature of improving the isolation insidethe device used for the high frequency amplification section bycontrolling the gate voltage of the device as necessary without addingcomponents or changing substrates, and increasing the dynamic range ofoverall gain of the EER high frequency amplifier. Therefore, it ispossible to increase the dynamic range of gain with a simple circuitconfiguration which is not different from the conventional EER highfrequency amplifier, so that it is possible to further improvecost-effectiveness of the EER high frequency amplifier. Hereinafter, anembodiment of the EER high frequency amplifier according to the presentinvention will be described. Components that are common in each drawingused in the embodiment will be assigned the same reference numerals, andduplicate description will be omitted.

FIG. 3 is a configuration diagram of the EER high frequency amplifieraccording to an embodiment of the present invention. In FIG. 3, EER highfrequency amplifier 1 has:envelope detecting section 2 that detects theenvelope of an inputted high frequency signal and extracts the amplitudecomponent; limiter 3 that extracts the phase component from the inputtedhigh frequency signal; baseband amplification section 4 that amplifiesthe amplitude signal separated into the amplitude component by envelopedetecting section 2; high frequency amplification section 5 that isformed with depression-type GaAs FET 5 a and amplifies the phase signalseparated into the phase component and performs amplitude modulationusing the amplitude signal amplified by baseband amplification section 4as a power supply; and gate voltage control section 6 that controls thegate voltage of GaAs FET 5 a in high frequency amplification section 5.

Next, the operation of EER high frequency amplifier 1 shown in FIG. 3will be described. When a high frequency signal is inputted to EER highfrequency amplifier 1, envelope detecting section 2 detects the envelopeof the high frequency signal to extract the amplitude component, andlimiter 3 extracts the phase component from the high frequency signal.Then, baseband amplification section 4 generates a voltage according tothe amplitude signal included in the amplitude component inputted fromenvelope detecting section 2 and provides that voltage as the powersupply voltage of the drain (D) of GaAs FET 5 a in high frequencyamplification section 5. This drain voltage is constantly monitored bygate voltage control section 6. When the drain voltage becomes lower (orhigher) than a predetermined reference voltage, gate voltage controlsection 6 makes gate voltage Vgs variable and increases or decreases theisolation between the input and the output of GaAs FET 5 a.

For example, when the drain voltage of GaAs FET 5 a is lower than thefirst reference voltage, gate voltage control section 6 decreases gatevoltage Vgs to increase the isolation between the input and the outputof GaAs FET 5 a, and, when the drain voltage is higher than the firstreference voltage and up to a predetermined voltage, makes the gatevoltage proportional to the drain voltage, and carries out normalamplification control. Further, when the drain voltage of GaAs FET 5 ais higher than the second reference voltage which is set at a highervoltage level than the first reference voltage, gate voltage controlsection 6 decreases gate voltage Vgs to increase the isolation betweenthe input and the output of GaAs FET 5a, and, when the drain voltage islower than the second reference voltage and higher than the firstreference voltage, makes the gate voltage proportional to the drainvoltage, and carries out normal amplification control. By carrying outgate voltage control in this way, the isolation between the input andthe output of GaAs FET 5 a is controlled, and the dynamic range of gainin high frequency amplification section 5 is improved.

FIG. 4 is a characteristic diagram showing a relationship of the gain(Gain) to the gate voltage (Vgs) of GaAs FET realized by EER highfrequency amplifier 1 of FIG. 3. That is, the characteristic diagram ofFIG. 4 shows fluctuation of the gain (Gain) when the drain voltage (Vds)of GaAs FET 5 a is fixed at 0 V and the gate voltage (Vgs) is madevariable.

Generally, in EER high frequency amplifier 1, it is ideal that there isno coupling between the input and the output of GaAs FET 5 a when thedrain voltage (Vds) of GaAs FET 5 a is 0 V, and therefore, when thedrain voltage (Vds) is 0 V, the smaller gain (Gain) GaAs FET 5 a has,the better. In other words, the bias voltage for operating GaAs FET 5 aas a saturated amplifier (that is, gate voltage (Vgs) ) is approximatelyVgs=−1.3 V, and therefore, as shown in the characteristic diagram ofFIG. 4, by making the gate voltage (Vgs) of GaAs FET 5 a variable from−1.3 V to 0 V, the gain (Gain) is reduced from −14 dB to −28 dB byapproximately 14 dB. By this means, the amount of reduction in gain(Gain) indicates the degree of improvement of the isolation when thedrain voltage (Vds) is 0 V.

FIG. 5 shows an example of a circuit configuration inside gate voltagecontrol section 6 of FIG. 3. As shown in FIG. 5, an internal circuitryof gate voltage control section 6 has first operational amplifier 7,second operational amplifier 8, drain voltage determining section 9 anda plurality of resistances around. Therefore, the operation of gatevoltage control section 6 will be described with reference to FIG. 3 andFIG. 5. The output voltage of baseband amplification section 4 (that is,drain voltage) is amplified at first operational amplifier 7 and secondoperational amplifier 8 to provide the gate voltage (Vgs) of GaAs FET 5a in high frequency amplification section 5, and a drain voltage (Vds)is constantly monitored by drain voltage determining section 9.

When drain voltage determining section 9 detects that the drain voltage(Vds) of GaAs FET 5 a is lower than (or higher than) the referencevoltage (Vref), gate voltage control section 6 starts controlling thegate voltage (Vgs). That is, when the drain voltage is lower than thefirst reference voltage (Vref), the initially set gate voltage (Vgs) isheld, and, when the drain voltage is higher than the first referencevoltage (Vref) and lower than the predetermined voltage, the gatevoltage (Vgs) is controlled in proportion to the drain voltage (Vds).When the drain voltage is higher than the second reference voltage(Vref) which is higher than the first reference voltage, the initiallyset gate voltage (Vgs) is held, and, when the drain voltage is lowerthan the second reference voltage (Vref) and higher than the firstreference voltage, the gate voltage (Vgs) is controlled in proportion tothe drain voltage (Vds).

By controlling the gate voltage (Vgs) of GaAs FET 5 a in this way, it ispossible to increase the dynamic range of the gain (Gain) by increasingor decreasing the isolation between the input and the output of GaAs FET5 a without interfering amplification operation in the range of normaluse. In FIG. 5, although a case has been shown where diode D is used asdrain voltage determining section 9, other devices having the samefunction can be obviously used. Further, a drain voltage determiningsection may adopt other circuit configurations having the same function.It is also possible to directly use an output signal (that is, amplitudesignal) of the envelope detecting section as a signal inputted to drainvoltage determining section 9. Further, although a GaAs FET has beendescribed as an example of the device used for the high frequencyamplification section, other devices having the same function can beobviously used.

The operation of gate voltage control section 6 is not limited to theabove-described gate voltage control, and, for example, gate voltagecontrol section 6 may control the gate voltage in inversely proportionto the drain voltage and control the isolation between the input and theoutput of GaAs FET 5 a, thereby making it possible to improve thedynamic range of gain in high frequency amplification section 5. Whengate voltage control section 6 controls the gate voltage so as to beproportional to the logarithm of the drain voltage, or controls the gatevoltage so as to be inversely proportional to the logarithm of the drainvoltage, it is also possible to control the isolation between the inputand the output of GaAs FET 5 a, so that the dynamic range of gain inhigh frequency amplification section 5 can be improved.

FIG. 6 is a characteristic diagram as a result of experiment ofimproving the dynamic range when the circuit of the gate voltage controlsection as shown in FIG. 5 is used in EER high frequency amplifier 1,where the horizontal axis indicates the drain voltage (Vds) and thevertical axis indicates the gain (Gain). As shown in FIG. 6, when thegate voltage (Vgs) is not controlled (Vgs not controlled), even if thedrain voltage (Vds) decreases to lower than 0.1V, the gain (Gain)decreases only to approximately −13 dB. However, when the gate voltage(Vgs) is controlled (Vgs controlled), and the drain voltage (Vds) is0.001V, the gain (Gain) decreases to approximately −29 dB, and, when thedrain voltage (Vds) decreases to lower than 0.1V, the gain (Gain)decreases to approximately −20 dB. That is, by controlling the gatevoltage, the isolation improves by approximately 16 dB, and, as aresult, the dynamic range of gain (Gain) of the high frequency amplifierimproves by approximately 16 dB.

The present application is based on Japanese Patent Application No.2004-273890, filed on Sep. 21, 2004, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

As described above, by using the EER high frequency amplifier of thepresent invention, it is possible to further improve the isolationinside the device used for the high frequency amplification section.Therefore, the EER high frequency amplifier of the present invention canbe applied not only to base station apparatus and terminal equipment inmobile communication, but also to digital terrestrial televisiontransmitters and high-speed wireless data communication apparatus.

1. An EER modulation amplifier that outputs a desired modulated andamplified signal from a high frequency amplification section byseparating a phase signal and an amplitude signal from an inputted highfrequency signal, amplifying the signals individually, and controlling adrain voltage of the high frequency amplification section based on theamplified amplitude signal, the EER modulation amplifier comprising: adrain voltage generating section that generates a drain voltageaccording to the amplitude signal and supplies the drain voltage to adrain terminal of the high frequency amplification section; a drainvoltage determining section that determines a magnitude of the drainvoltage generated by the drain voltage generating section in comparisonto a predetermined reference voltage; and a gate voltage control sectionthat controls a gate voltage of the high frequency amplification sectionaccording to the magnitude relationship between the reference voltageand the drain voltage determined by the drain voltage determiningsection.
 2. The EER modulation amplifier according to claim 1, wherein:the reference voltage is formed with a first reference voltage and asecond reference voltage which has a higher voltage level than the firstreference voltage; and the gate voltage control section holds aninitially set gate voltage when the drain voltage is determined to belower than the first reference voltage, and controls the gate voltage inproportion to the drain voltage when the drain voltage is determined tobe higher than the first reference voltage and lower than the secondreference voltage.
 3. The EER modulation amplifier according to claim 2,wherein the gate voltage control section holds an initially set gatevoltage when the drain voltage is determined to be higher than thesecond reference voltage, and controls the gate voltage in proportion tothe drain voltage when the drain voltage is determined to be lower thanthe second reference voltage and higher than the first referencevoltage.
 4. The EER modulation amplifier according to claim 1, whereinthe drain voltage determining section directly detects the amplitudesignal separated from the high frequency signal and determines themagnitude of the amplitude signal in comparison to the referencevoltage, instead of determining the magnitude of the drain voltage incomparison to the reference voltage.